If it is true I can understand why they want to bring him back, and perhaps they could find a way to make it work but it would be extremely hard. If they bring him back as dark-side Vader it undoes his whole redemption story and if they bring him back as light-side Vader he probably wouldn't be as cool.

Lets not forget all the crazy rumors for the prequels. Wasn't one that Charlton Heston was going to play a young Yoda? Seriously. Without any info every rumor is going to be examined.

I been thinking of plot ideas. Nazi were a strong inspiration for the Empire. Perhaps years after the Empire there is a surgence of Neo-Nazi style Empire/Sith inspired cult. It would allow for the use of the Sith imagery without the original characters.

Lucas's original scripts has a full army of Sith Lords. That would be a way of using that idea. The Rule of Two was ended with Sidious and Vader. But now there is a group of Wanna be Sith Lords. Seeing a full out war among Sith and Jedi would certainly be something we have never seen.